This invention relates generally to the formation of an impervious layer in a soil structure, and more specifically, to a generally vertically oriented barrier which can be used to isolate a source of contaminated groundwater. The invention is particularly useful in sealing off a contaminated dump site by surrounding the site with a continuous vertical layer of substantially impervious material.
The use of slurry walls to create a subsurface barrier which is vertically oriented is well known. Trenches, which may be formed by any of several means, are filled with a mixture of bentonite clay and water to temporarily support the walls of the trench until concrete is pumped into the trench displacing the slurry. Such subsurface walls rely on the concrete material to prevent the flow of fluids across the trench. However, due to the rigid nature of hardened concrete, and the likelihood that soil adjacent to the concrete will shift with substantial force, such concrete barrier walls are unreliable as a truly impervious barrier to the flow of contaminated groundwater.
Furthermore, it is often difficult to obtain access to areas surrounding an existing contaminated landfill. The prior art techniques of forming a slurry trench and subsequently filling that trench with concrete require substantial surface area in which to operate. In fact, in areas surrounding landfills which have been in existence for several years, the space requirements of prior art techniques make the formation of vertical barrier walls impossible.
A particularly useful form of sheet materia useful in creating a barrier in accordance with the present invention is shown and described in U.S. Pat. No. 4,501,788, and its European counterpart patent No. 0059625, which patents are incorporated herein by reference. The sheet comprises a support coated with a layer of bentonite. The support is a flexible porous fabric capable of venting gas to which the bentonite adheres. The support may be a woven polypropylene mat and the sheet may also have a fabric scrim covering to protect it during transport, handling and installation. A series of sheets can be installed with a minimal overlap to form a barrier of almost any shape.
Accordingly, it is a primary object of the present invention to provide a method for forming an impervious barrier to the flow of contaminated groundwater from existing leaking landfills.
Another object of the invention is to provide an effective barrier against the flow of contaminated groundwater through soil structures which will withstand substantial movement of soil within the structure.
A further object of the invention is to provide an economical and effective apparatus for installing a barrier against the flow of contaminated fluids in a soil structure.
A further object of the invention is to provide a barrier to the flow of contaminated fluids which is substantially less permeable as compared to conventional barrier forming techniques.
Yet another object of the invention is to provide a method and apparatus for installing an impermeable sheet in a slurry filled trench.
Yet another object of the invention is to provide a barrier for use in soil structures which includes sheets of impervious material, the perimeter areas of which form joints against adjacent material which are effective barriers against the flow of contaminated fluid.